Many materials such as thermoplastic film, woven fabric from polymeric yarn, and flattened plastic tubing are manufactured in a sheet-like form and in order to form a useful end product from the material it is necessary to seal the sheet-like material to itself or to a similar material. If the material is thermoweldable or heat fusible it may be sealed to itself or to a similar material by the application of energy which raises the temperature of the material to its welding or fusing temperature. Thermoplastic sheets made from materials such as polyethylene, polypropylene, polyvinyl chloride, vinylidene chloride copolymers, etc. are readily heat sealable or heat weldable; and, in the prior art, sealing or welding has been accomplished by mechanically pressing two sheets of thermoplastic film together between heated seal bars and applying radio frequency energy, and by applying heated and compressed air blown through opposed nozzles to seal the material together. In addition to radio frequency energy, other sources of radiant energy have been employed to seal together thermoplastic materials. One such energy source is the laser described in U.S. Pat. No. 3,560,291 which issued on Feb. 2, 1971 to A. J. Foglia et al. The Foglia et al patent shows the bonding of thermoplastic resin film using radiation from a laser source. In another prior art disclosure, the laser welding of plastic tubes is described in U.S. Pat. No. 3,769,117 which issued on Oct. 30, 1973 to William Edmund Bowen et al. An additional application of laser energy to the processing of thermoplastic materials is a method of forming a tear line in a multilayer laminate as described in U.S. Pat. No. 3,790,744 which issued to William Edmund Bowen on Feb. 5, 1974. However, in all of these prior art methods which employ laser energy to seal thermoplastic materials, the energy is applied with the beam focused to a point. This requires that in order to seal in a line the beam must be scanned or moved across the area to be sealed or the material must be moved in a longitudinal or in a transverse direction so that the focal point of the beam traces a line. The movement of material longitudinally through the point of a beam is illustrated quite clearly in the aforementined patent to Bowen, U.S. Pat. No. 3,790,744, where in FIG. 1 thereof themoplastic film is continuously moved through the focal point of a beam in order to form a line of weakness in the film. However, it takes a relatively long period of time to move a point or spot across material having commercially usable widths and such long periods are greater than can be practically tolerated in a manufacturing process.
Accordingly, an object of the present invention is to provide a method and apparatus of welding together heat sealable materials with laser energy wherein the laser beam does not have to be moved or scanned across the material to be sealed or the material does not have to be moved through a stationary beam.
Another object of the present invention is to increase the speed of sealing thermoplastic materials with a laser beam.
The accomplishment of the foregoing and other objects will be apparent to those skilled in the art from the following Summary of The Invention, Drawings, and Detailed Description of the Preferred Embodiment.